1. Field of the Invention
The present invention relates to a display device, in particular, a display device whose display color on a display surface side can be changed by allowing a liquid to inflow into or outflow from an inside of a small pore of a porous body, and relates to an electrical apparatus using the display device.
2. Description of Related Art
Conventionally, as image displays using display devices that display information such as letters and images, image displays of non-light-emission types that utilize external light such as light from illumination devices and sunlight, and image displays of light-emission types that do not utilize external light or the like have been provided. The above-described image displays of non-light-emission types include liquid crystal displays of transmission types, reflection types and the like. Whereas, the image displays of light-emission types include plasma display panels, electro luminescence panels and field emission displays.
However, the above-described image displays of either light-emission types or non-light-emission types using the conventional display devices cannot allow users to recognize textures like white papers. That is, the conventional display devices cannot achieve white display with sufficient display quality, and it is afraid that high-definition display cannot be achieved.
For example, JP 4(1992)-48349 B suggests the use of an opaque porous body that is colored in white or a pastel color, as a sheet material composing a display surface, in a display device of a first conventional example. Moreover, in this display device of the first conventional example, a liquid for display having a refractive index that is close to a refractive index of the porous body is prepared, and is applied on a surface of the porous body according to the information to be displayed. Furthermore, in the display device of the first conventional example, the liquid penetrates small pores of the porous body, so as to decrease a light reflectance of the display surface with respect to external light and make the display surface to be partly transparent, so that the information can be displayed by a base that is provided beneath the porous body.
In addition, display devices of second and third conventional examples include a display device of an electroosmosis system, which moves a liquid by applying an electric field to a porous body, as respectively described in JP 61(1986)-59491 B and JP 63(1988)-36512 B, for example.
More specifically, in the display devices of the second and third conventional examples, a liquid impregnation rate of the surface of the opaque or colored porous body is controlled so as to scatter external light, whereby a light reflectance and a light transmittance thereof with respect to external light can be controlled. Moreover, in these display devices of the second and third conventional examples, the refractive index of the porous body is made to be equal to the refractive index of the transparent liquid in advance, so that the porous body can be transparent by filling insides of through holes (small pores) of the porous body with the liquid, and can reflect the external light by allowing the liquid to outflow from the through holes.
However, in the above-described display devices of the first to third examples, the opaque or colored porous body is used, and thus it is sometimes difficult for the display devices to improve the display quality of the white display and to achieve the high-definition display. That is, in these display devices of the conventional examples, external light is reflected by an interface between an inner wall surface of the porous body surrounding the small pore and air in the small pore, whereby the white display is achieved. However, in the case where the porous body is opaque, the external light that transmits the inside of the porous body from the inner wall surface is absorbed by the porous body, so that an efficiency to utilize the external light is decreased. Thus, in the case of using the opaque porous body, loss of light is likely to occur on the display surface, and the light reflectance of the display surface cannot be controlled with high precision. As a result, it becomes difficult to increase the display quality of the white display, and the high-definition display cannot be achieved. Particularly in the display device of the first conventional example, the small pores that are communicatively connected with one another are used in all over the inside of the porous body, and the liquid is applied on the surface of the porous body, so that it is difficult to improve not only the display quality of the white display but also display quality of other colors that are displayed by the above-described base.
Whereas, in the case where the porous body is colored, light that is colored in the color of the porous body is included in the light reflected by the inner wall surface, which causes degradation of color purity of white, and also degrades the display quality of the white display.
Moreover, a display device of a fourth conventional example adopts an electrowetting system that changes an interfacial tension of the liquid in the small pores by applying an electric field to the liquid, and moves the liquid by utilizing an electrowetting phenomenon (electrocapillary phenomenon) as described in JP 10(1998)-39799 A, for example.
More specifically, this display device of the fourth conventional example comprises transparent sheets, which include a first sheet, a second sheet and a third sheet that are arranged serially from the display surface side at a predetermined interval. An upper-side space is disposed between the first sheet and the second sheet, and a lower-side space is disposed between the second sheet and the third sheet. The upper-side space and the lower-side space are connected communicatively via two reservoirs that are disposed on the second sheet. Moreover, in the upper-side space, the lower-side space and the reservoirs, a colored liquid that is colored in a predetermined color and a transparent liquid are closed. Furthermore, in the display device of the fourth conventional example, a white sheet is disposed so as to cover a surface of the third sheet on the display surface side or a non-display surface side, and it achieves the white display. That is, the display device is structured so that the white display can be achieved on the display surface by using the white sheet, by moving the colored liquid into one of the two reservoirs and moving the transparent liquid into the upper-side space and the lower-side space.
However, in this display device of the fourth conventional example, the white sheet is exposed to the external light and the liquids all the time, and thus the color of the white sheet is likely to be changed to gray or the like over the course of time, which may lead to the degradation of the display quality of the white display. Moreover, the white sheet is required to be disposed on the third sheet that has the longest distance from the display surface. Therefore, it is difficult to increase the color purity of white and to improve the display quality of the white display.